Photophysics and photochemistry of natural waters with emphasis on radical probe development and application
type: CreativeWork
description: The work presented here consists of a literature review and calculations to estimate the importance of photochemistry to carbon cycling in the oceans, followed by a photophysical study of a series of stable nitroxide radical probes that have been used for the quantitative detection of individual carbon-centered radicals and reducing species in natural waters. Two appendices follow. The first contains preliminary experiments utilizing one of the nitroxide probes in an investigation of hydroxyl radical production rates and steadystate concentrations in seawater. The second consists of an investigation of the singlet lifetimes of humic acids (HA), in order to aid in understanding their photochemical cycling and nt1uence on other compounds. The impact of photochemical reactions on global oceanic carbon cycling was calculated from literature values. The results indicate that between 1 and 13% of all dissolved organic carbon in the oceans is oxidized photochemically. This is a significant flux term, much larger than that of riverine input for example. A photophysical study of nitroxide radical probes was undertaken. For all of the compounds studied, steady-state absorption and fluorescence spectra were identical to those of the parent fluorophores. A decrease in fluorescence lifetime and quantum yield of tens- to hundreds-fold was observed for the paramagnetic compounds relative to their diamagnetic counterparts. Very rapid fluorescence quenching rates (3 to 80 x 1010 s-1) were calculated for the fluorescamine moiety of the paramagnetic nitroxide compounds in a variety of solvents. Calculated energy minimized geometries were very similar for all compounds which implies that geometric differences are not responsible for the variations found m fluorescence lifetimes and quantum yields between compounds. Calculated Forster and Dexter overlap integrals do not support deexcitation by these mechanisms. Time-resolved absorption measurements resulted in no evidence for transient …
abstract: The work presented here consists of a literature review and calculations to estimate the importance of photochemistry to carbon cycling in the oceans, followed by a photophysical study of a series of stable nitroxide radical probes that have been used for the quantitative detection of individual carbon-centered radicals and reducing species in natural waters. Two appendices follow. The first contains preliminary experiments utilizing one of the nitroxide probes in an investigation of hydroxyl radical production rates and steadystate concentrations in seawater. The second consists of an investigation of the singlet lifetimes of humic acids (HA), in order to aid in understanding their photochemical cycling and nt1uence on other compounds. The impact of photochemical reactions on global oceanic carbon cycling was calculated from literature values. The results indicate that between 1 and 13% of all dissolved organic carbon in the oceans is oxidized photochemically. This is a significant flux term, much larger than that of riverine input for example. A photophysical study of nitroxide radical probes was undertaken. For all of the compounds studied, steady-state absorption and fluorescence spectra were identical to those of the parent fluorophores. A decrease in fluorescence lifetime and quantum yield of tens- to hundreds-fold was observed for the paramagnetic compounds relative to their diamagnetic counterparts. Very rapid fluorescence quenching rates (3 to 80 x 1010 s-1) were calculated for the fluorescamine moiety of the paramagnetic nitroxide compounds in a variety of solvents. Calculated energy minimized geometries were very similar for all compounds which implies that geometric differences are not responsible for the variations found m fluorescence lifetimes and quantum yields between compounds. Calculated Forster and Dexter overlap integrals do not support deexcitation by these mechanisms. Time-resolved absorption measurements resulted in no evidence for transient …
author: Herbelin, Sarah E.
language: en_US
keywords: Photochemistry, Carbon cycle, Argo Maine (Ship) Cruise, Weatherbird II (Ship) Cruise
date published: 1994-08
date modified: 2026-07-27T22:05:23Z
provider: Woods Hole Oceanographic Institute
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: Massachusetts Institute of Technology and Woods Hole Oceanographic Institution

PropertyValue
property ID: Handle
value: https://hdl.handle.net/1912/5560

PropertyValue
property ID: DOI
value: 10.1575/1912/5560